Mechanism Study Of Organizing High Efficiency Scavenging And Suppressing Super-knock In GDI Engine

The super-knock phenomenon in supercharged gasoline direct engine is triggered by the auto-ignition of hot-spot and the detonation of unburned mixture.The scavenging can reduce the in-cylinder thermal load and clear the super-knock origins,then the super-knock is eliminated.This paper studied the effect of engine structure and DVVT strategy on scavenging by numerical simulation,and investigated the effect of DVVT strategy on combustion characteristics by experimental study.The results showed that the piston pit with a shallow depth adjacent to the center of cylinder could intensify the scavenging flow,and less fresh charge flowed into exhaust port directly,then the scavenging was optimized.The effect of injector and spark plug on scavenging was minus due to the small volume.The scavenging efficiency and the ratio of cleared carbon particles were 99.5% and 61.7% separately.The least high-temperature residual gas and particles entered the next combustion cycle,and the super-knock possibility was the lowest.The effect of IVO on combustion was greater than that of EVC.With the advance of IVO,the intake pressure and injection mass increased,the spark timing and combustion phase retarded,power,BSFC,combustion duration and exhaust temperature also increased.In two early IVO conditions,when EVC retarded,the intake pressure,injection mass,power,BSFC,combustion pressue and exhaust temperature increased,combustion duration shortened.In three late IVO conditions,the combustion characteristics were unchanged with the postponement of EVC.The effect of IVO on scavenging and combustion was crucial,the scavenging was a vital factor to combustion.Organizing high efficiency scavenging could suppress super-knock and improve dynamic performance.Therefore scavenging had a vital significance to improve the engine performance.